| Association of homoeologous group 6 aneuploids with
leaf necrosis in hexaploid wheat varieties1),2) Rosalind MORRIS3), J. W. SCHMIDT3) and V. A JOHNSON4) SEARS (1954) first reported that Chinese Spring wheat plants nullisomic for chromosome 6B had necrotic patches on the leaves in some seasons, and that a telocentric for the short arm suppressed the necrotic condition. LATER (1966 and personal communication), he assigned the symbol co (corroded) to a locus on the short arm of 6B which was derived from some atom-bombed material provided by Luther SMITH. Because of its origin SEARS considered the co locus to be a deficiency. If this is so, the necrotic phenotype in both materials is due to the absence of a gene concerned with normal leaf development. In the course of developing monosomic and other aneuploid conditions in the hard red winter wheat varieties, Wichita and Cheyenne, we have observed leaf necrosis involving the group 6 chromosomes. The necrosis occurred on seedlings in the greenhouse in the winter during the 7-week vernalization period at 4.4-7.2C during the night and sometimes warming to a maximum of 13C with sunlight during the day. No artificial lights were used during this period, so that only 8 to 10 hours of low-intensity daylight were available. Some plants monosomic for 6A, 6B or 6D in both varieties had leaf necrosis which was evident at the one- to two-leaf stage. The only other aneuploid type in Cheyenne was a plant having one complete 6B chromosome and a telocentric for the long arm which usually formed a heteromorphic bivalent. This plant was necrotic and would be monosomic for the short arm. In the variety Wichita, we have obtained nullisomics for all the group 6 chromosomes. Seeds for 6A nullisomics were kindly supplied by Dr. A. MOCHIZUKI, Kobe University, Japan. Leaf necrosis was observed on 45 nullisomics for 6B, 4 nullisomics for 6A, and 11 out of 13 nullisomics for 6D. A monotelosomic for 6A was necrotic. One monoisosomic for 6D also was necrotic, but monotelosomics, ditelosomics, and a monoisosomic for 6D derived from a different misdivision event showed no evidence of necrosis. These results suggest that opposite arms of 6D are involved in the two situations, and that one arm contains a necrosissuppressing gene. For 6B, the following aneuploids besides the nullisomics have been (obtained : monotelosomic, ditelosomic and monoisosomic for the short arm (all of which had normal leaves except for one monotelosomic which was slightly necrotic) ; ditelosomic and di-isosomic for the long arm (all of which showed some leaf necrosis) . These observations agree with those of SEARS for Chinese Spring that the short arm of 6B is needed to suppress necrosis. We also have observed plants with a heteromorphic bivalent for 6B, where the telocentric involved the long arm. Some of these plants displayed leaf necrosis. It may be that, with the low temperatures and low-intensity lighting under which the seedlings of these aneuploids were grown, the hemizygous condition of the genes for normal development cannot always prevent necrosis . However, there is less consistency of effect than in the case of nullisomics, where the normal genes are completely absent. These observations suggest that one arm of each of the group 6 chromosomes has a gene(s) which suppresses leaf necrosis but that one dose of the gene is not always sufficient. Literature Cited SEARS, E. R. 1954. The aneuploids of wheat. Missouri Agr. Expt. Sta. Res. Bull. 572 : 58. SEARS, E. R. 1966. Chromosome mapping with the aid of telocentrics. Proc. Second Intern. Wheat Genetics Symp. Lund, Sweden. Hereditas Suppl. Vol. 2 : 370-381. (Received October 30, 1969) |
| 1) Cooperative investigations of the Department of Agronomy,
University of Nebraska, Lincoln, Nebraska, and the Crops Research Division.
Agricultural Research Service, U.S. Department of Agriculture, Lincoln,
Nebraska. Published with the approval of the Director as Paper No. 2711,
Journal Series, Nebraska Agr. Exp. Sta., U.S.A. 2) This study was supported in part by the Agricultural Research Service, U.S. Department of Agriculture, Cooperative Agreement No. 12-14-100-8425(34), administered by the Crops Research Division, Beltsville, Maryland, U.S.A. 3) Department of Agronomy, Nebraska Agricultural Experiment Station, Lincoln, Nebraska, U.S.A. 4) Crops Research Division, Agricultural Research Service, U.S. Department of Agriculture, Lincoln, Nebraska, U.S.A. |